The invention relates generally to the sampling of moving fluids such as moving airflows, and more particularly to a sampling system that extracts samples of a moving fluid passing thereover. The moving fluid as a medium may represent a variety of gases. Matter to be sampled may represent solid particles or liquid droplets or other material physically or chemically distinguishable from the suspension medium.
As an example, airflows may be sampled in support of a variety of flow monitoring applications for determining aerosol content, or conforming microbiological presence, using standard microbiological techniques. The Dry Filter Unit (DFU) 1000 represents an exemplary air sampling device for collecting, for example, bio-particulates from suspension in ambient air for analysis. The DFU-1000 provides a pressure differential to draw air within, thereby enabling particles to be collected. Note that “ambient air” corresponds in this document to nominal temperature of 20° C. (degrees Celsius) and pressure of 101 kPa (kilopascals).
Particles smaller than a specific size may be categorized under an Environmental Protection Agency standard as specified under Title 40 of the Code of Federal Regulations (CFR). For example, particle measurement PM-10 under 40 CFR §50.6(c) corresponds to particles having effective diameters no larger than 10 μm (microns). Similarly, PM2.5 under 40 CFR §50.7(a)(1) corresponds to particles no larger than 2.5 μm. FIG. 1A shows an exemplary isometric view of the DFU-1000.
The DFU-1000 houses a pump/blower and is configured in a one-person portable carrying case for 40,000 hour-life continuous duty. The DFU-1000 may use commercially available power at 120/240 VAC (volts) from alternating current at 50/60 Hz (hertz) or else direct current sources adaptable using an optional auxiliary power pack of 24 VDC. The DFU-1000 has dimensions of 15 in (inches) high, 13 in wide and deep, a mass of 42 lbm (pounds-mass). The power requirements are 5.6 A (amps) at operation and 17 A starting at 120 VAC.
The DFU-1000 may be conventionally equipped with an open-top tandem-chamber inlet assembly 100 shown in FIG. 1B in isometric view as an exploded diagram. Air flows over a top-facing orifice 110 into which particulate matter descends entrained in an air stream at low velocity to an entrance chamber 120. The air stream passes from the entrance chamber 120 through a forked pair of twin filter chambers 130 and rejoins in an exit chamber 140 to enter a top port of the DFU-1000, which draws in the air.
Each of the twin chambers 130 houses a cylindrical filter holder 150 that secures a polyester mesh filter 155 having a diameter of approximately 1.5 in. Each chamber 130 incorporates a foam seal 135 to avoid pressure drop losses between the inlet 110 and the exit 140. The filter 155 traps particles larger than those that pass through its mesh. The resulting collection from the filter 155 may include particles of interest for further analysis as well as others larger than desired but collaterally entrapped nonetheless.
The holder 150 may comprise two halves 160, 165 pivotably connected to a molded hinge 170 and securable together when closed by a latch 175. The holder 150 may be opened by disconnecting the latch 175 to remove and replace the filter 155. Contents collected on the removed filter may then be analyzed at a separate facility. When the holder 150 is open, the filter 155 may be inserted into recesses 180, one of which being equipped with baffles that prevent the filter 155 from being dislodged by the pressure differential produced by the DFU-1000.
Artisans of ordinary skill will recognize that the air intake described for the DFU-1000 represents an example application, and will recognize that other devices for drawing or otherwise moving fluid medium to enable particulate matter collection may be contemplated, accordingly.